Audio speakers are extensively utilized in automobiles to generate acoustic signals from the automotive radio. It is often desired to improve the quality of the speakers in an automobile. This is typically accomplished by replacing the speakers in the automobile with speakers which are amplified by having an amplifier supported by or connected directly to the speaker. A power control circuit and method for selectively supplying power from a constantly available power source to the audio amplifier has been used. The control circuit uses a differential input to produce a control signal by sensing the existence of an audio signal at the input to the radio amplifier by determining the difference in potential between the input leads. A switching means is utilized to close a power switching circuit to power the audio amplifier from the power source in response to the control signal so that the power amplifier does not receive power in the absence of an audio input signal.
The disadvantage with such a control circuit is that at low potential differences between the input leads, the differential sensing means will not operate to produce the control signal. Therefore, the potential difference between the input leads must be at a reasonable value in order to operate the differential sensing means to produce an amplified output response for the audio amplifier. In other words, once the audio radio initially sends an audio signal to the power control circuit, an acoustic audio signal will not be produced until the potential of the audio signal from the audio radio is large enough to operate the differential sensing means. Thus, the audio amplifier will not automatically receive power once the audio radio initially sends an audio signal.